Is an acid etching gel necessary for dental bonding?

Etching is an essential part of bonding. The tooth surface needs to be microscopically roughened by etching in order for bonding to be permanent. Without etching, bonding just falls off. Older bonding systems were composed of separate etching gel, primer and bonding agents. Over time, manufacturers have produced newer systems that combine these into fewer steps. While the newer systems save time, some studies have shown that the older systems that use separate etching gel and primer actually produce stronger bonds.

now a days many single step [ primer + etching] kits are available in the market . so if yr dentist is using that than no separate etching is required.

Every dentist has a preferred bonding system that may or may not utilize a separate acid etch prior to placement of the bonding agent.  Several generations of bonding agents have a combined etch, primer and bond agent in the same bottle.  Typically when I perform dental bonding I will bevel the surrounding tooth to gain extra surface area to adhere to as well as assisting in the blending of the filling into the tooth.  I will typically apply an etch to the enamel to try to gain a little extra bonding strength.  It could be ineffective bonding, but your "hard bite" combined with the fact that he is lengthening the tooth for you could very easily be the cause as well.  I would discuss your concerns with him.  It cold be that something likes veneer or crown may be more appropriate to achieve your desired result.